Detecting cell phone presence.

Hey guys, I made a car keypad here: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1236735887

And it works great, but now I'm thinking about other ways of interfacing with the arduino in my car door.

What I had in mind was something along the lines of the iFob at SparkFun: http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=135

But instead of using the Nike transmitter, I would like it to somehow know when my phone is nearby. I have a Palm Pre, which has both WiFi and bluetooth. My first thought is to have the arduino interfaced with a BlueGiga, and then react when my phone syncs to it (or just tries to). I wouldn't want my phone to actually sync with the device over a headset profile or streaming audio, as that would interfere with me using the phone. Unfortunately, my phone doesn't support any serial port profiles. I usually don't have my bluetooth radio on, so I'd probably just toggle it on long enough to get recognized.

Does anyone have any experience with this type of thing (detecting bluetooth IDs), or a better solution altogether?

It looks like using the INQUIRY command to the BlueGiga makes it respond with the addresses of all bluetooth devices visible, per the iWRAP3 User Guide, page 28-31.

I could send this request every 10.5 seconds, and have my arduino react when the incoming serial text contains my bluetooth address eg: 00:10:c6:62:bb:9b.

Well, it's not quite what you're talking about, but the Blimpduino has something that will detect cell phone signals and navigate itself to the source. Maybe you could use something along those lines..